New boiler

[SaladDodger]

Hi

A quick enquiry regarding a new boiler.

I currently have a Baxi open vent boiler, which is about 25 years old. I'm getting fed up with it breaking down every year when I most need it, so I'm looking to replace it with a similar open vent boiler. I don't want a combi, our mains flow isn't good enough though the pressure is ok. We also have two bathrooms and having looked them up it would seem that perhaps a combi is not our best get.

I'm not looking to undermine the installer or anything, but I like to know what I'm going into and to do a bit of research before I spend a couple of grand on a new one.

My one at the moment is 15kw, which was fine before we had the extension, but now seems slightly underpowered. We have 13 radiators, though two are half size, so maybe 12 normal size ones. (10 before the extension). We have a four bedroom detached 1980 house with two large rooms downstairs, double glazing, cavity wall insulation.

I've done the boiler sizing thing on the FAQ page and it comes out at 19kw. I realise that a boiler should be correctly specified to be most efficient, but if I was to go for an 18kw one, would it run the risk of being overused and have a harder life, thus having reduced longevity than if I went for a 24kw or 28kw model? I accept they wouldn't be as efficient so would use more fuel, but I wondered if they would be more reliable in the long term? I'm not sure how it works? I'm less worried about the fuel costs but would rather have slightly better reliability and longevity (wouldn't everyone).

Regarding makes, this is obviously quite a subjective issue. Having looked at Which it seems keen on Worcester Bosch and Vaillant and something like the Vaillant Ecotec 418/428 would seem around the right ball park. Again I'll have to be guided by the installer but it's nice to have some idea before I go into anything.

Am I on the right lines?

 

[Dan Robinson]

Balls to Which magazine. Their advise is no less subjective than the advice given here.

Intergas
Atag
Vaillant

In that order.

 

[dcawkwell]

Hi

A quick enquiry regarding a new boiler.

I currently have a Baxi open vent boiler, which is about 25 years old. I'm getting fed up with it breaking down every year when I most need it, so I'm looking to replace it with a similar open vent boiler. I don't want a combi, our mains flow isn't good enough though the pressure is ok. We also have two bathrooms and having looked them up it would seem that perhaps a combi is not our best get.

I'm not looking to undermine the installer or anything, but I like to know what I'm going into and to do a bit of research before I spend a couple of grand on a new one.

My one at the moment is 15kw, which was fine before we had the extension, but now seems slightly underpowered. We have 13 radiators, though two are half size, so maybe 12 normal size ones. (10 before the extension). We have a four bedroom detached 1980 house with two large rooms downstairs, double glazing, cavity wall insulation.

I've done the boiler sizing thing on the FAQ page and it comes out at 19kw. I realise that a boiler should be correctly specified to be most efficient, but if I was to go for an 18kw one, would it run the risk of being overused and have a harder life, thus having reduced longevity than if I went for a 24kw or 28kw model? I accept they wouldn't be as efficient so would use more fuel, but I wondered if they would be more reliable in the long term? I'm not sure how it works? I'm less worried about the fuel costs but would rather have slightly better reliability and longevity (wouldn't everyone).

Regarding makes, this is obviously quite a subjective issue. Having looked at Which it seems keen on Worcester Bosch and Vaillant and something like the Vaillant Ecotec 418/428 would seem around the right ball park. Again I'll have to be guided by the installer but it's nice to have some idea before I go into anything.

Am I on the right lines?

Glow worm system boiler no one has vented system any more.
With a 15 year warranty. You'll probably have to upgrade your hot water tank to a tank with a modern high recovery coil.

 

[FiremanT]

Glow worm system boiler no one has vented system any more.

????????

 

[vulcancontinental]

Glow worm system boiler no one has vented system any more.
With a 15 year warranty. You'll probably have to upgrade your hot water tank to a tank with a modern high recovery coil.

Rubbish. Nothing wrong with Open Vent. If your boiler has lasted 25 years there isn't much wrong with your system either.

All Dan's suggestions are too exotic and too expensive. IMO.

 

[diverdee]

baxi solo and magnaclean just stay open vented much cheaper

 

[dcawkwell]

Glow worm system boiler no one has vented system any more.
With a 15 year warranty. You'll probably have to upgrade your hot water tank to a tank with a modern high recovery coil.

Rubbish. Nothing wrong with Open Vent. If your boiler has lasted 25 years there isn't much wrong with your system either.

All Dan's suggestions are too exotic and too expensive. IMO.

Sadly they don't make them like they used to.

 

[D_Hailsham]

I've done the boiler sizing thing on the FAQ page and it comes out at 19kw. I realise that a boiler should be correctly specified to be most efficient, but if I was to go for an 18kw one, would it run the risk of being overused and have a harder life, thus having reduced longevity than if I went for a 24kw or 28kw model? I accept they wouldn't be as efficient so would use more fuel, but I wondered if they would be more reliable in the long term?

The method given in the FAQ assumes that the rads are the correct size.

Use the Whole House Boiler Size Calculator to find out what size boiler you really need.

There is no point installing a larger boiler than necessary. It's not like a car, where a 5 litre engine turning over at 1000rpm at 60mph will last longer that a 1 litre running at 4000 rpm to achieve the same speed.

Furthermore an oversized boiler would use almost the same amount of fuel as the correctly sized one. This is because both boilers will adjust the amount of fuel used to meet the current requirement.

 

[DP]

Cannot see why a simple boiler like yours keeps breaking down. Perhaps might be an idea to change your service engineer and start upgrading piece by piece thus each step means better use of fuel with cost spread out over a period of time. When the boiler really, really, REALLY does break down, simple change is all that would be needed then

 

[SaladDodger]

I've done the boiler sizing thing on the FAQ page and it comes out at 19kw. I realise that a boiler should be correctly specified to be most efficient, but if I was to go for an 18kw one, would it run the risk of being overused and have a harder life, thus having reduced longevity than if I went for a 24kw or 28kw model? I accept they wouldn't be as efficient so would use more fuel, but I wondered if they would be more reliable in the long term?

The method given in the FAQ assumes that the rads are the correct size.

Use the Whole House Boiler Size Calculator to find out what size boiler you really need.

There is no point installing a larger boiler than necessary. It's not like a car, where a 5 litre engine turning over at 1000rpm at 60mph will last longer that a 1 litre running at 4000 rpm to achieve the same speed.

Furthermore an oversized boiler would use almost the same amount of fuel as the correctly sized one. This is because both boilers will adjust the amount of fuel used to meet the current requirement.

Ok I understand that. Actually the idhee test was the one I did that came out at 19kw. So I might as well stick with the closest one to that figure.

 

[D_Hailsham]

Actually the idhee test was the one I did that came out at 19kw. So I might as well stick with the closest one to that figure.

Now you need to check that you have 19kW worth of rads.

Unfortunately radiator output is not a fixed quantity, like an electric fire, it varies with three temperatures: water in (flow), water out (return), and air.

Rad specs assume these are: 75C, 65C, and 20C, which was OK for old non-condensing boilers, but not for modern condensing boilers which need a 20C difference between flow and return. There is also the fact that a boiler does not condense if the return temperature is above 55C.

This means you need to know the rad output when: flow = 75C, return = 55C, and air temp = 20C. The maths is a bit complicated, so I won't bore you with it, but the answer is that the rad will only produce 85% of the output shown in the catalogue. This means you have to install rads which are 17% larger, or 20-25% to be on the safe side (very cold weather).

You can use the Stelrad Catalogue to estimate the output of your rads at the standard temps (75,65,20). Use the Elite table headed 50 Δt.